Final answer:
Generally, to thicken one cup of liquid, about 1 tablespoon of cornstarch is needed for a standard consistency. If a thicker consistency is desired, up to 2 tablespoons may be used.
Step-by-step explanation:
To thicken one cup of liquid with cornstarch, you generally need between 1 to 2 tablespoons of cornstarch. The amount can vary depending on the desired thickness and the type of liquid you are thickening. For a standard thickness, about 1 tablespoon of cornstarch is sufficient, making option (a) the correct choice. If you need a thicker consistency, you might want to go up to 2 tablespoons.